This invention relates to a process for the production of micro-organisms. Many micro-organisms are known which can utilise hydrocarbons as their carbon and/or energy source. The dried biomass obtainable by the cultivation of such micro-organisms, often referred to as single cell protein, is rich in protein and can be used as a possible food-stuff or food supplement for man and animals.
A process for the cultivation of hydrocarbon-utilising micro-organisms usually comprises the growth of such organisms under aerobic conditions in a liquid growth medium comprising, in addition to the carbon source, assimilable sources of nitrogen, such as nitrogen (N.sub.2) gas, nitrate-ions, ammonium-ions or urea. Although nitrogen gas is cheaply available the use thereof as source of nitrogen is disadvantageous in that much energy is required to metabolise it which makes it rather expensive on the carbon-source utilised by the micro-organisms. Nitrate-ions are also expensive on the carbon source as they have to be reduced to ammonium-ions in order to become metabolisable by the micro-organisms. Ammonium-ions are both cheaply available and not expensive on the carbon-source but have the draw-back of being inhibitory to the growth of many organisms, particularly certain methanol- and methane-utilising bacteria, when being present in the liquid growth medium in too high a concentration. Finally urea, which is also cheaply available and is not expensive on the carbon-source, can only be utilized by a restricted number of bacterial species.
It is an object of the present invention to provide an improved process for the cultivation of hydrocarbon-utilising micro-organisms whereby the disadvantages inherent in the use of certain sources of nitrogen are overcome.